linux-kernel - Re: [PATCH 1/3] signal: sys_rt_sigtimedwait: simplify the timeout logic

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Date:	Mon, 25 Apr 2011 19:56:05 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Nikita V. Youshchenko" <nyoushchenko@...sta.com>,
	Matt Fleming <matt@...sole-pimps.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] signal: sys_rt_sigtimedwait: simplify the timeout
	logic

On 04/25, Linus Torvalds wrote:
>
> On Mon, Apr 25, 2011 at 10:26 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > If only I knew what this comment could say except
> >
> >        /* Why do we add (tv_sec || tv_nsec) ?  */
> >
> > I'd better send 4/3 which simply removes this (I hope) unneeded code.
>
> It's to guarantee that timeout is at least one tick more than asked
> for, because the rule is that you really have to wait for AT LEAST the
> time asked for.

Aah, thanks. This makes sense. I'll add the comment.

> So "+ (tv_sec || tv_nsec)" is just the "+1" for the "not zero timeout" case.

So, we have

	timeout = timespec_to_jiffies(ts) + (tv_sec || tv_nsec);
	...

	if (timeout)
		timeout = schedule_timeout_interruptible(timeout);

Perhaps it makes sense to turn this code into

	timeout = timespec_to_jiffies(ts);

	if (timeout)
		// make sure we sleep at least the time we asked for
		timeout = schedule_timeout_interruptible(timeout + 1);

Assuming that timespec_to_jiffies() always returns nonzero if ts is
"not zero timeout". I think it does.

Oleg.

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